The present invention relates to a method of providing numerical values indicative of the pulse repetition frequency and the pulse-to-pulse period of a pulse train after each pulse of the pulse train which may have varying periods under certain circumstances, and a device for implementing the method.
Rotational velocities can be measured by pulse generators which generate pulse trains whose frequencies are proportional to the rotational velocities. Precise sensing of the speed can be achieved by measuring the time period elapsing between two consecutive pulses. To this end, clock pulses of an oscillator which issues a clock pulse train with constant frequency are being counted. When it is desired to calculate the rotational speeds by using these counted values, reciprocal values will have to be formed.
A method for the determination of velocity is known from the published German application No. 30 08 876, wherein the counting of clock pulses is initiated by the measured pulse of a pulse converter until the number of clock pulses corresponds to a presettable number. The counting action is then continued until the next pulse of a presettable number of measured pulses occurs. The desired velocity value is determined from the ratio of the total number of counted clock pulses to the defined number of measured pulses. According to this method, speed determination can be attained by division only. It is desired in many cases to sense velocities with great accuracy. Numbers with several digits are to be processed under such circumstances. These numbers can be divided in a relatively short time only when complex circuit configurations are being used. With relatively little expenditure in circuit schemes, there ensue long periods of calculation due to the sequential processing of the individual digits.
The period of calculation is frequently limited by the interval between two consecutive pulses issued by a pulse generator that senses the velocity. In the event that the velocity varies within a wide range, differently long periods are available for the calculating operations. Velocities that are variable within wide ranges occur, for instance, when sensing the effects of rotation of vehicle wheels. In vehicles incorporating anti-skid control devices, the rotational speeds are monitored by sensors arranged at the wheels. In a device known from the published British application No. 2,052,901 corresponding to U.S. Pat. No. 4,335,431 issued June 25, 1982 to Junichi Takahashi for preventing the locking of a wheel during braking, a sensor arranged on the drive shaft is connected via pulse-former circuits to input circuits which communicate with the bus of a microprocessor. Further, memories and counters are connected to the bus. The bus comprises a data bus, an address bus and a control bus. In between two consecutive pulses of the sensor, the clock pulses of a clock generator are summed up in counters. The rates of counted values which occurred during several pulse periods are stored in a series of registers from which they are called off by the microprocessor for the speed calculation. With each pulse of the sensor, an interrupt is demanded from the microprocessor. The interrupt releases the speed calculation when the calculation period required is shorter than the pulse period. However, if the pulse period is shorter than a predetermined period that is sufficient to perform the calculation, the interrupt signal will be rendered inoperative by masking until the calculating operation has been completed. Only the following non-masked interrupt signals will result in a new speed calculation. At high rotational speeds of wheels, this method does not use all pulses of the sensor for the speed calculation, so that some important information may be irretrievably lost.